InputText: Actually flip the is_keyboard_hidden flag properly

MultiInputDialog does a close -> show in the same callback,
so if we don't actually keep it in sync with the actual state, we lose
the keyboard and essentially softlock the UI, which is Very Bad(TM).

NOTE: InputDialog has its own keyboard_hidden flag, and it looks...
fairly nightmarish.

frontend/ui/widget/inputtext.lua

@@ -64,7 +64,7 @@ local InputText = InputContainer:extend{
     for_measurement_only = nil, -- When the widget is a one-off used to compute text height
     do_select = false, -- to start text selection
     selection_start_pos = nil, -- selection start position
-    is_keyboard_hidden = false, -- to be able to show the keyboard again when it was hidden
+    is_keyboard_hidden = true, -- to be able to show the keyboard again when it was hidden. (On init, it's the caller's responsibility to call onShowKeyboard, as far as we're concerned, it's hidden)
 }
 
 -- These may be (internally) overloaded as needed, depending on Device capabilities.
@@ -132,9 +132,8 @@ local function initTouchEvents()
             if self.parent.onSwitchFocus then
                 self.parent:onSwitchFocus(self)
             else
-                if self.is_keyboard_hidden == true then
+                if self.is_keyboard_hidden then
                     self:onShowKeyboard()
-                    self.is_keyboard_hidden = false
                 end
             end
             -- zh keyboard with candidates shown here has _frame_textwidget.dimen = nil.
@@ -677,8 +676,12 @@ dbg:guard(InputText, "onTextInput",
 
 function InputText:onShowKeyboard(ignore_first_hold_release)
     Device:startTextInput()
-    self.keyboard.ignore_first_hold_release = ignore_first_hold_release
-    UIManager:show(self.keyboard)
+
+    if self.is_keyboard_hidden then
+        self.keyboard.ignore_first_hold_release = ignore_first_hold_release
+        UIManager:show(self.keyboard)
+        self.is_keyboard_hidden = false
+    end
     return true
 end